This invention relates to a new tool turret mechanism and more particularly to a twin disc tool turret mechanism for CNC machines with two tool-mounting discs attached separately to a toothed ring-type three piece registration and lock-up coupling device (commercially designated as Curvic or Hirth coupling, hereinafter referred to as "three piece coupling device"). By a special arrangement for tool placement, this mechanism allows doubling of tool quantity on a tool turret without increasing the turret size.
At present, most NC lathes have one or two tool turrets on which a number of either outside (OD) turning or inside (ID) boring tools are mounted. Cutting tools are mounted on a symmetric polygon or circular disc which indexes (including rotating, registering and locking) at the same angulars interval according to the number of tools mounted. The registration and locking mechanism, essential to reproduce the exact coordinate location of the cutting tools, generally uses either a two-piece or a three-piece toothed ring-type coupling device. For machining operations, the desired tool is selected by the indexing mechanism to take up the active position of the tool turret, then the entire turret on a carriage is moved to engage the active tool with the workpiece. Because all tools are mounted on the turret, inactive tools may make contact (interfere) with the workpiece and the workpiece-holding chuck before and/or during the machining operation. This interference may be reduced by special arrangements of tools in relation to the workpiece but cannot be totally eliminated. Therefore, the programmer of the lathe has to take interference into consideration.
On a conventional tool turret, the quantity of tools can be increased only by increasing the size of the tool mounting disc. Increasing the disc size, however, makes the turret heavier, thus harder to move, and a larger disc also slows down the speed of disc rotation. Besides, for any given disc rotational speed, increasing the quantity of tools also increases the average time required for tool changes. For all the reasons mentioned above, the number of tools on most conventional tool turrets is restricted to twelve.
In order to reduce tool interference and to increase tool quantity, the tool turret may be replaced with a single tool holding post, having an automatic tool changing mechanism similar to that of machining centers. This approach, however, is much more complicated and, therefore, more costly than a conventional tool turret.
In addition, a popular factor in recent years is to include a live spindle to perform some secondary machining operations after turning. Provision of touch sensing probes on a tool turret for on-the-machine and in-process measurement of workpiece diameter is also gaining popularity on some newly introduced machines.
All the aformentioned problems are solved and all the desirable functions are provided by this subject invention, which for the sake of generalization is hereby designated as a "Twin Disc Tool Turret Mechanism".